Modem technologies to transmit digital data over the Public Switched Telephone Network (PSTN) have made rapid advances in recent years. The latest such technologies, such as the CCITT V.32, V.32bis specifications and ITU successor organization to the CCITT! V.34 (which was known during its gestation phase as V.FAST) specification require a "training" interval during the initial connection phase of operation before communication can begin, to test and responsively compensate for imperfections in the telephone channel or line performance. If audio monitoring of the telephone line is turned on, the user of a modern digital computer modem placing a call can often hear the training phase as a "feep-foop" sound followed by a "rushing water" sound just after the remote modem answers.
This training interval may last from 3 to 10 or more seconds in various circumstances. With conventional methods, no transfer of information, particularly including voice conversation, is possible during the training interval. In accordance with the present invention, on the other hand, ordinary conversation can proceed while the training is simultaneously occurring. Once training has been completed, the operation can switch to a purely digital mode, by which means the audio conversation may continue while simultaneously also transferring other digital data. Such operation is greatly facilitated by modern audio coding techniques, which significantly reduce the amount of digital data which must be transferred for a given perceived speech fidelity.
The importance of the present invention may be more fully appreciated when one considers the possibility of an advanced PSTN instrument having the ability to transmit both voice and data and operating in an underlying purely digital mode. Such an instrument, however, could be objectionable to ordinary telephone users for ordinary calls because of the frustrating training delay required just after a call is answered. Improving the instrument by incorporating the present invention, however, possibly taking advantage of techniques disclosed in my prior U.S. Pat. Nos. 5,036,513 and 5,136,586, results in functionality transparent or imperceptible to the user as compared to an ordinary telephone; i.e., conversation can begin immediately as soon as the phone is answered. It can be expected that the delay between initiation of the call and full digital operation will be somewhat longer with the current invention as compared to present methods wherein the line is fully dedicated to training for a period of time; however, this represents attractive tradeoff from the point of view of any ordinary telephone user who is not required to change his habits.
In this patent, a method and system are disclosed proprietarily referred to as "Omniphone".TM., for telephone line multiplex channeling of toll-quality voice and modem-encoded digital data from telecommunication devices (FAX, computers, displays, printers, etc.). During the connection phase as specified by this method, voice signals are divided into successive time frames each of which is time compressed by a certain percentage; and, in accordance with the present invention, filling the resulting unoccupied time within each such frame with test signals instead of telecommunication device data as per U.S. Pat. No. 5,136,586. On receipt of these test signals (which may include silence) the receiving station may deduce properties of the particular telephone channel which has been obtained. Thus, by means of the present invention, training for the digital mode is also occurring as well as supporting the user conversation; and when sufficient information about the channel has been obtained, the training is said to be completed and operation may switch to a purely digital mode. Throughout this entire process, the user's conversation continues unaffected. After the switchover, arbitrary digital information, such as text strings, faxes, computer data, or pictures and the like may be transferred, consistent with the speed of the digital modem technology, the audio coding technology employed, etc.
The technique of my earlier U.S. Pat. No. 5,036,513 can also be important insofar as it enables seamless operation with ordinary phones (achieving only ordinary telephone functionality in that mode, of course). In accordance with that technique, there is provided a novel method of and apparatus for voice communication and transparent, non-interfering, automatic digital data exchange between appropriately equipped telephone terminals having cooperative digital signal processing and visual display equipment, Using special recognition signal protocol triggering signals and providing modem capability for FAX, printer, microprocessor, answer machines and the like for providing extended services using in-band signaling sensible by users and machines. Such method is useful both with ordinary telephone exchanges and ISDN type exchanges.
The term "training" as applied to high speed digital modems and as before briefly mentioned, means determining the transfer function of the particular telephone channel or line which has been obtained (in the most interesting case, over the PSTN), so that a compensator may operate to neutralize the effect of these imperfections. These imperfections may include phase changes, reflections (echoes), delays, and frequency emphasis or de-emphasis, among other things.
To ascertain these imperfections, present day international standard modem technologies, such as the before-referenced V.32, V.32bis and V.34, specify a training interval during which certain known test signals are transmitted and the received signal analyzed. During the period these test signals are exchanged, however, no other information (particularly no voice communication) can flow over the connection--the problem which the present invention seeks to alleviate or obviate. The net effect, then, is to achieve a "train-while-talk" capability.